I would guess that she might have been egg bound and or suffered a temporary prolapsed vent while she was trying to lay. The egg may have broken inside, but either way, something triggered the others to peck her vent and cause bleeding. Clean her up as best you can. Ask parents if you can get some calcium tablets with vitamin D or Tums, and give her one daily for about 3 days in a row. If using Tums, break them into small pieces, but the calcium tablet can be given orally in one piece, just popped into the back of her beak. That may help if her egg shells are thin or if she has a prolapse.